Lightly brush one tablespoon olive oil on the cut sides of the rolls and lemon halves; set aside.,Combine remaining oil and vinegar in a small bowl.,Brush a little of mixture on zucchini and onion, then season with salt and pepper.,Grill zucchini and onion, over medium heat, until tender, about 2 to 3 minutes per side.,Meanwhile toast rolls, cut side down, about 3 minutes.,______